The present invention relates generally to grain drying equipment and more particularly to an improved low profile continuous crossflow column grain dryer with optimum dryer air recirculation within the grain column and automatic self cleaning heat plenum chamber.
It is generally believed that continuous crossflow dryers, that is, those dryers which have wet grain continually entering the dryer and dried grain continually exiting the dryer with drying air passing across the flowing column of grain, were not suitable for drying grains having a high moisture content. The reason for the difficulties experienced in the use of conventional continuous crossflow dryers was that they only operated at their optimum design performance over a fairly narrow band of moisture removal range due to fixed design conditions such as a fixed cooling air flow, and a fixed heated air flow.
At a grain moisture removal of 6 to 8 percentage points, most conventional dryers work satisfactorily. The cooling rate is matched fairly well with the drying rate. The grain column is usually split 25-35 percent cooling and 65-75 percent heating. The total blower horsepower is normally split to be 30-40 percent cooling and 60-70 percent drying. Dryers with 25 percent cooling column usually use the upper extreme in cooling horsepower, thus operating the cooling plenum at a higher static pressure that the heating plenum and delivering 50-100 percent more cool air per bushel than drying air.
Under conditions wherein grain coming from the field is very high in moisture, and the drying rate is slowed significantly, the grain in such prior art systems was over cooled, which is not a particular problem from the standpoint of the quality of the grain dried, but it does waste considerable energy. Under very dry grain inlet conditions wherein the moisture removal is in the 3-5 percentage range, grain flow rate is very high and cooling is inadequate. If grain conditioned by such a process is to be stored in a non-aerated storage and therefore has to be cooled considerably after being dried in the dryer, the only reasonable solution was believed to be to cut back on the drying temperature to drastically slow down the drying rate to the point at which the grain retention time in the cooling zone was adequate to cool the grain. It is well known that the efficiency of the drying process is reduced and the fuel cost is very high when the plenum operating temperature of a cross flow dryer is significantly reduced. It is also well known that the grain to be stored in non-aerated storage cannot be too hot or it will deteriorate. There is, therefore, the need for a continuous flow drying apparatus which will overcome these problems found with prior art devices.
Another weakness with most conventional continuous crossflow column grain drying devices is that when drying grains under conditions where cooling the grain in the dryer is not desired, the cooling air flow must be blocked off and the cooling grain column is of little or no value in drying. There is, therefore, a need for equipment of this type which will adequately compensate for this situation by having a design that can be easily adjusted to provide drying of grain in the grain column area normally used for cooling to maximize the performance and capital investment of the dryer.
It is also known that crossflow dryers are normally: (1) of a full pressure design, using positive pressure in a heating as well as a cooling plenum, or (2) designed with suction cooling and pressure heating. But, they do not in one common structure embody the capability to perform in either method with quick and easy adjustment between the methods, a management capability thought to be highly desirable, especially in farming regions where grain sorghum (milo) or sunflowers (both of which are crops with abnormally high combustible seed coat particles which accumulate in the heat plenums of dryers that recirculate the suction cooling air through the burner, causing fires in the dryer plenum or grain column) plus other cereal grain crops are grown in one farming operation. Having a dryer capable of being easily converted in a matter of a few minutes would allow full pressure heating and cooling of milo, sunflowers, or other crops with flammable residue, to be dried with pressure heating and cooling using only ambient air with no recycled exhaust air. Then, when it is desirable to dry corn, wheat, soybeans or other safer crops with residue that is considerably less flammable, the dryer can be adjusted for suction cooling plus recycling of the recycling of the less humid portion (approximately half) of the exhaust heated air, thus, reducing fuel consumption by 35 to 50 percent of the fully pressurized and cool process fuel costs, while not significantly affecting drying capacity.